With the rapid development of display technology, the technology for semiconductor elements which is a core of the display apparatus has also progressed rapidly. For the existing display apparatus, an Organic Light Emitting Diode (referred to as OLED), as a current type light emitting device, has been widely used in the field of high performance display field more and more because of its characteristics of self emission, fast response, wide viewing angle and capability of being fabricated on a flexible substrate, etc.
The OLED can be divided into two types according to driving manners, that is, a Passive Matrix Driving OLED (referred to as PMOLED) and an Active Matrix Driving OLED (referred to as AMOLED). Because the AMOLED display has advantages such as low manufacturing cost, high response speed, energy saving, being applicable in DC drive for portable devices, wide working temperature range and the like, it has a prospect of replacing liquid crystal display (referred to as LCD) to become a next generation new-type flat panel display. In the existing AMOLED display panel, each OLED comprises a plurality of Thin Film Transistor (referred to as TFT) switch circuits. Among them, amorphous silicon TFT has been widely used in the field of liquid crystal display, a matrix image sensor, etc., as a kind of important electronic devices, because of its excellent static electricity characteristics.
However, instability of the amorphous silicon TFT is always a problem to be solved in the known technical scheme. One of the main instability of the amorphous silicon TFT is in that a threshold voltage of the TFT would shift in a condition of a DC gate bias applied for a long time. For example, in a high voltage area (greater than 25V generally), the shift of the threshold voltage is due to a shielding for a gate electric field after traps in an insulating layer trap charges; in a low voltage area (generally an operation voltage of the amorphous silicon TFT), the shift of the threshold voltage is due to a generating or removing of a dangling bond states caused by the bias voltage in an active layer. The shift of the threshold voltage will cause a decrease of a luminance of the AMOLED display, which will affect uniformity of brightness in the display. In addition, the TFTs in the AMOLED would be in the bias state for a long time during the operation status, which would speed up a decay rate of the TFTs and reduce a lifespan of the display apparatus.